MEMS Devices and Fabrication Methods Thereof

ABSTRACT

A method for fabricating a MEMS device includes providing a micro-electro-mechanical system (MEMS) substrate having a sacrificial layer on a first side, providing a carrier including a plurality of cavities, bonding the first side of the MEMS substrate on the carrier, forming a first bonding material layer on a second side of the MEMS substrate, applying a sacrificial layer removal process to the MEMS substrate, providing a semiconductor substrate including a second bonding material layer and bonding the semiconductor substrate on the second side of the MEMS substrate.

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/650,867, filed Oct. 12, 2012, and entitled “MEMS Devices andFabrication Methods Thereof,” which application is hereby incorporatedherein by reference.

BACKGROUND

Micro-electro-mechanical systems (MEMS) are the technology of formingmicro-structures with mechanical and electronic features. The MEMSdevice may comprise a plurality of elements (e.g., movable elements) forachieving mechanical functionality. In addition, the MEMS device maycomprise a variety of sensors that sense various mechanical signals suchas pressure, inertial forces and the like, and convert the mechanicalsignals into their corresponding electrical signals.

For example, a MEMS device having an accelerometer may comprise a proofmass, which is attached to the structure of the MEMS device. In responseto the influence of external accelerations, the proof mass may deflectfrom its neutral position and move relative to the structure of the MEMSdevice. A sensor is employed to detect the relative motion between theproof mass and the structure of the MEMS device. In addition, the sensormay generate an electrical signal proportional to the motion strength ofthe proof mass.

In order to reduce the cost of manufacturing and packaging of MEMSsystems, MEMS systems may comprise both micromechanical devices andelectronic circuits. More particularly, the micromechanical devices andthe electronic circuits such as complementary metal oxide semiconductor(CMOS) devices may be fabricated in the same manufacturing process andboth devices may be bonded together through suitable bonding techniquessuch as eutectic bonding and the like.

MEMS applications include motion sensors, pressure sensors, printernozzles and the like. Other MEMS applications include inertial sensorssuch as accelerometers for measuring linear acceleration and gyroscopesfor measuring angular velocity. Moreover, MEMS applications may extendto optical applications such as movable minors, and radio frequency (RF)applications such as RF switches and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1A illustrates a cross-sectional view of a MEMS in accordance withan embodiment;

FIG. 1B illustrates a cross-sectional view of another MEMS in accordancewith an embodiment;

FIG. 1C illustrates a cross-sectional view of another MEMS in accordancewith an embodiment;

FIG. 1D illustrates a cross-sectional view of another MEMS in accordancewith an embodiment;

FIG. 2 illustrates a cross-sectional view of a semiconductor devicehaving a plurality of openings in a dielectric layer formed over asubstrate in accordance with an embodiment;

FIG. 3 is a cross sectional view of the semiconductor device illustratedin FIG. 2 after an oxide deposition process has been applied to thedielectric layer side of the wafer in accordance with an embodiment;

FIG. 4 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 3 after a plurality of opening are formed in thedielectric layer in accordance with an embodiment;

FIG. 5 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 4 after a polysilicon layer is formed on the dielectriclayer in accordance with an embodiment;

FIG. 6 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 5 after a low stress nitride layer is formed on thedielectric layer as well as the polysilicon layer in accordance with anembodiment;

FIG. 7 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 6 after an oxide deposition process is applied to the lowstress nitride layer in accordance with an embodiment;

FIG. 8 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 7 after a polysilicon layer is formed on the oxide layerin accordance with an embodiment;

FIG. 9 illustrates a cross sectional view of a carrier in accordancewith an embodiment;

FIG. 10 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 9 after an etching process is applied to the carrier anddeep openings are formed in the substrate of the carrier in accordancewith an embodiment;

FIG. 11 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 10 after an oxide layer is deposited in the openings andon the surface of the semiconductor device in accordance with anembodiment;

FIG. 12 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 11 after an etching process is applied to the carrier inaccordance with an embodiment;

FIG. 13 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 12 after an oxide removal process is applied to thecarrier;

FIG. 14 illustrates a cross sectional view of a semiconductor devicehaving a MEMS device stacked on top of a carrier;

FIG. 15 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 14 after a thinning process, an oxide deposition processand a polysilicon deposition process are performed to the MEMS device inaccordance with an embodiment;

FIG. 16 illustrates the formation and patterning of a bonding materiallayer on top of the MEMS device in accordance with an embodiment;

FIG. 17 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 16 after the MEMS device's structure is defined inaccordance with an embodiment;

FIG. 18 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 17 after a vapor HF process is applied to the MEMS devicein accordance with an embodiment;

FIG. 19 illustrates the formation and patterning of a bonding materiallayer on the CMOS device in accordance with an embodiment;

FIG. 20 illustrates a cross sectional view of a semiconductor devicehaving a CMOS device stacked on top of a MEMS device in accordance withan embodiment;

FIG. 21 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 20 after a grinding process is applied to thesemiconductor device in accordance with an embodiment;

FIGS. 22-44 illustrate intermediate steps of fabricating a MEMS devicein accordance with another embodiment;

FIGS. 45-52 illustrate intermediate steps of fabricating a MEMS devicein accordance with another embodiment;

FIG. 53 illustrates a cross sectional view of a semiconductor device inaccordance with another embodiment;

FIG. 54 illustrates a cross sectional view of a semiconductor device inaccordance with yet another embodiment;

FIG. 55 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 54 after a patterning process is applied to thenon-bonding side of the carrier in accordance with an embodiment; and

FIG. 56 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 55 after a conductive material is deposited to formelectrical readout structures in accordance with an embodiment.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the variousembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the present embodiments are discussed in detailbelow. It should be appreciated, however, that the present disclosureprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the embodimentsof the disclosure, and do not limit the scope of the disclosure.

The present disclosure will be described with respect to embodiments ina specific context, a micro-electro-mechanical system (MEMS) device. Theembodiments of the disclosure may also be applied, however, to a varietyof electrical or mechanical semiconductor devices. Hereinafter, variousembodiments will be explained in detail with reference to theaccompanying drawings.

FIG. 1A illustrates a cross-sectional view of a MEMS in accordance withan embodiment. The MEMS 10 includes a MEMS device 100, a carrier 200 anda CMOS device 300. As shown in FIG. 1, the MEMS device 100 is sandwichedbetween the carrier 200 and the CMOS device 300. Suitable bondingtechniques such as fusion bonding, eutectic bonding and the like may beemployed to bond the MEMS device 100, the carrier 200 and the CMOSdevice 300 together.

The CMOS device 300 may include a substrate. In accordance with anembodiment, the substrate of the CMOS device 300 may be formed ofsilicon. Alternatively, the substrate of the CMOS device 300 may beformed of other semiconductor materials including silicon germanium(SiGe), silicon carbide and the like. Furthermore, other substrates thatmay be used include multi-layered substrates, gradient substrates,hybrid orientation substrates and any combinations thereof.

The CMOS device 300 may include active and passive devices (not shown).As one of ordinary skill in the art will recognize, a wide variety ofactive and passive devices such as transistors, capacitors, resistors,combinations of these, and the like may be used to generate thestructural and functional requirements of the design for the MEMS 10.The active and passive devices may be formed using any suitable methods.

The MEMS device 100 may comprise a substrate having MEMS features andfunctionality. The substrate of the MEMS device 100 may have similarmaterials as the substrate of the CMOS device 300, although thesubstrate of the CMOS device 300 and the MEMS device 100 are notnecessary to be the same material. The CMOS device 300 is bonded on topof the MEMS device 100. According to an embodiment, the bonding processmay be implemented by using eutectic bonding. In other embodiments, thebonding process may include other suitable bonding techniques such asfusion boding, thermo-compression bonding, direct bonding, glue bondingor the like.

The carrier 200 includes a substrate having a plurality of cavities. Inaccordance with an embodiment, the substrate of the carrier 200 may beformed of silicon. Alternatively, the carrier 200 may be formed ofsuitable materials including a ceramic substrate, a quartz substrate andthe like.

The carrier 200 may include active and passive devices. As one ofordinary skill in the art will recognize, a wide variety of active andpassive devices such as transistors, capacitors, resistors, combinationsof these, and the like may be used to generate the structural andfunctional requirements of the design for the MEMS 10. The active andpassive devices may be formed using any suitable methods.

As shown in FIG. 1A, the MEMS device 100 as well as the CMOS device 300are boned together and further bonded on top of the carrier 200. Inaccordance with an embodiment, the MEMS device 100 and the carrier 200may be bonded together through suitable bonding techniques such asfusion bonding.

FIG. 1B illustrates a cross sectional view of another MEMS in accordancewith an embodiment. The structure of the MEMS 15 is similar to that ofthe MEMS 10 shown in FIG. 1A except that one additional thin structurelayer is formed between the MEMS device 100 and the CMOS device 300. Oneadvantageous feature of having the thin structure layer is that softout-of-plane structures such as springs may be formed by the thinstructure layer. Such a thin structure layer helps to improve thedimension of the MEMS 15 while keeping easy movements along the Z axisof the MEMS 15.

FIG. 1C illustrates a cross sectional view of another MEMS in accordancewith an embodiment. The structure of the MEMS 17 is similar to that ofthe MEMS 10 shown in FIG. 1A except that a plurality of vias 21, 23 and25 are formed between a poly-silicon structure 506 and a bondinginterface layer 802 of the MEMS device 100. More particularly, the vias21, 23 and 25 are formed in an oxide layer 702. It should be noted thatthe poly-silicon structure 506 may function as a bottom electrode of theMEMS device 100.

One advantageous feature of having the vias 21, 23 and 25 in the oxidelayer 702 is that the vias 21, 23 and 25 can prevent noise fromaffecting the MEMS device 100. In particular, the bonding interfacelayer 802 may be formed of poly-silicon and connected to a ground planeas a shielding plane through the vias 21, 23, 25 in the oxide layer 702.By adopting the bonding interface layer 802 as a ground shielding plane,some noise issues such as parasitic capacitive coupling can be avoided.

FIG. 1D illustrates a cross sectional view of another MEMS in accordancewith an embodiment. The structure of the MEMS 19 is similar to that ofthe MEMS 15 shown in FIG. 1B except that a plurality of vias 31, 33 and35 are formed in the MEMS device 100. The function of the vias 31, 33and 35 is similar to that of the vias 21, 23 and 25 shown in FIG. 1C,and hence is not discussed again herein.

FIGS. 2-8 illustrate intermediate steps of fabricating a MEMS device inaccordance with an embodiment. FIG. 2 illustrates a cross-sectional viewof a semiconductor device having a plurality of openings in a dielectriclayer formed over a substrate in accordance with an embodiment. Thesubstrate 202 may be formed of silicon, silicon germanium, siliconcarbide or the like. The substrate 202 may be formed of low resistivesilicon. Alternatively, the substrate 202 may be a silicon-on-insulator(SOI) substrate. The SOI substrate may comprise a layer of asemiconductor material (e.g., silicon, germanium and the like) formedover an insulator layer (e.g., buried oxide and the like), which isformed in a silicon substrate. In addition, other substrates that may beused include multi-layered substrates, gradient substrates, hybridorientation substrates and the like.

A dielectric layer 204 is formed on top of the substrate 202. Thedielectric layer 204 may be formed, for example, of a low-K dielectricmaterial, such as silicon oxide. The dielectric layer 204 may be formedby any suitable deposition techniques known in the art, such asspinning, chemical vapor deposition (CVD) and plasma enhanced chemicalvapor deposition (PECVD) and the like.

FIG. 2 further illustrates the patterning of the dielectric layer 204 toform openings 206 in the dielectric layer 204. The patterning processmay be accomplished by depositing a commonly used mask material (notshown) such as photoresist over the dielectric layer 202. The maskmaterial is then patterned and the dielectric layer 202 is etched inaccordance with the pattern to form the openings 206.

FIG. 3 is a cross sectional view of the semiconductor device illustratedin FIG. 2 after an oxide deposition process has been applied to thedielectric layer side of the substrate in accordance with an embodiment.As shown in FIG. 3, the oxide may be employed to seal off the upperterminals of the openings 206. The oxide deposition may be formed usinga deposition process such as CVD or the like. More particularly, bycontrolling the deposition process, the material of the oxide layer maybe deposited in a non-conformable manner. In other words, the materialsof the oxide layer may build up on the upper terminal of the openingfaster than along the sidewalls and the bottom of the opening. Thisprocess leads to the formation of an overhang at the edge of the upperterminal of the opening and, as the deposition process continues, theoverhangs will merge, thereby sealing off the upper terminal of theopening to form a plurality of seams 302.

As shown in FIG. 3, the seams 302 are embedded in the oxide layer 204.In accordance with an embodiment, the oxide layer 204 is a sacrificialoxide layer of a MEMS device. During a releasing process of the MEMSdevice, the seams 302 help to reduce the releasing time of the MEMSdevice.

FIG. 4 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 3 after a plurality of opening are formed in thedielectric layer in accordance with an embodiment. A patterning processmay be applied to the dielectric layer 204 to form a plurality ofopenings 402. The patterning process may be accomplished by depositing acommonly used mask material (not shown) such as photoresist over thedielectric layer 204. The mask material is then patterned and thedielectric layer 204 is etched in accordance with the pattern.

According to the fabrication processes of the MEMS device 100, the oxideside of the substrate is thinned until a desired thickness is achieved.In accordance with an embodiment, the thickness of the oxide layer 204is in a range from about 0.5 um to about 5 um. The thinning process maybe implemented by using suitable techniques such as grinding, polishingand/or chemical etching. In accordance with an embodiment, the thinningprocess may be implemented by using a chemical mechanical polishing(CMP) process. In a CMP process, a combination of etching materials andabrading materials are put into contact with the oxide side of thesubstrate and a grinding pad (not shown) is used to grind away a portionof the oxide layer 204 of the substrate until the desired thickness isachieved.

FIG. 5 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 4 after a polysilicon layer is formed on the dielectriclayer in accordance with an embodiment. The polysilicon layer 502 isformed on the dielectric layer 204 through suitable fabricationtechniques such as CVD. The polysilicon layer 502 may be of a thicknessin a range from about 0.1 um to about 2 um.

The polysilicon layer 502 may be patterned to form functional elementssuch as electrodes and routing structures (e.g., polysilicon structure506). In addition, an over-etch process may be employed to formmechanical bumps (e.g., bump 504). It should be noted the polysiliconstructure 506 may function as bottom electrodes of the MEMS device. Asshown in FIG. 5, the electrodes are further coupled to the substratethrough a plurality of polysilicon vias. One advantageous feature ofhaving the polysilicon layer 502 shown in FIG. 5 is that the electricalconnection between the bottom electrodes and the substrate can be formedwithout a deep silicon etching process.

It should be noted that while a single polysilicon layer 502 isillustrated, those skilled in the art will recognize that multiplepolysilicon layers could be employed. Alternatively, an appropriateconducting material could likewise be employed for form the electrodesand routing structures shown in FIG. 5.

FIG. 6 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 5 after a vapor hydrogen fluoride (HF) stop layer isformed on the dielectric layer as well as the polysilicon layer inaccordance with an embodiment. Before the vapor HF stop layer isdeposited on the semiconductor device, another oxide deposition processmay be applied to the semiconductor device. In particular, an oxidelayer is deposited so that the electrodes 506 as well as the mechanicalbumps 504 are covered by the oxide layer. An etch-back process isapplied subsequently. As a result, the surface of the electrode 506 isexposed and the mechanical bump 504 is still covered by the oxide layer.

After the etching-back process has been applied to the semiconductordevice shown in FIG. 6, the vapor HF stop layer may be formed on thepolysilicon side of the semiconductor device. In accordance with anembodiment, the vapor HF stop layer may be a low stress nitride layer.Alternatively, the vapor HF stop layer may be formed of other suitablematerials such as SiC, AN, Al₂O₃ and the like. Throughout thedescription, the vapor HF stop layer may be alternatively referred to asa low stress nitride layer. The low stress nitride layer 602 may bedeposited on dielectric layer 204 through suitable fabricationtechniques such as CVD, Low-Pressure CVD (LPCVD) and the like.

FIG. 7 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 6 after an oxide deposition process is applied to the lowstress nitride layer in accordance with an embodiment. An oxide layer702 is further formed on the low stress nitride layer 602, asillustrated in FIG. 7. The oxide layer 702 may be formed by using wellknown deposition techniques such as CVD, or using some otherconventional techniques. The oxide layer 702 has a flat surface. If asufficiently flat surface is not obtained by the oxide deposition orformation process, flatness can be achieved by employing a CMP processor an etch-back process, as are known in the art.

FIG. 8 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 7 after a polysilicon layer is formed on the oxide layerin accordance with an embodiment. A bonding interface layer 802 isdeposited over the oxide layer 702. In accordance with an embodiment,the bonding interface layer may be formed of polysilicon. Alternatively,the bonding interface layer 802 may be formed of any suitable bondingmaterials such as silicon, amorphous silicon, silicon doped withimpurities, any combinations thereof and the like. The polysilicon layer802 is formed on oxide layer 702 through suitable fabrication techniquessuch as CVD, PVD and the like. The polysilicon layer 802, the oxidelayer 702 and the low stress nitride layer 602 may be patterned to formthe channels connected to air cavities (not shown) of a MEMS device.

FIGS. 9-13 illustrate intermediate steps of fabricating a carrier inaccordance with an embodiment. FIG. 9 illustrates a cross sectional viewof a carrier in accordance with an embodiment. The carrier may comprisea silicon substrate 902. As shown in FIG. 9, a dielectric layer 904 maybe formed on the top surface of the substrate 902. In accordance with anembodiment, the dielectric layer 904 may be a thermal oxide layer formedby performing a thermal oxidation on the carrier.

FIG. 10 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 9 after an etching process is applied to the carrier anddeep openings are formed in the substrate of the carrier in accordancewith an embodiment. As shown in FIG. 10, a Deep Reactive-Ion Etching(DRIE) process is performed to form deep openings 1002 in the substrate902. It should be noted that due to etching loading effects, the wideopenings at the edges of the cell (e.g., openings 1004 and 1006) aredeeper than the narrow openings in the center and middle of the cell(e.g., opening 1002).

FIG. 11 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 10 after an oxide layer is deposited in the openings andon the surface of the semiconductor device in accordance with anembodiment. The oxide layer 1102 may be formed by any suitable oxidationprocesses such as wet or dry thermal oxidation process, CVD or the like.An etching process, such as a reactive ion etch (RIE) or other dry etch,an anisotropic wet etch, or any other suitable anisotropic etch orpatterning process, is performed to remove the bottom portion of theoxide layer 1102. As a result, the bottom portions of the openings 1002are free from oxide. As shown in FIG. 11, the sidewalls of the openingsare protected by the oxide layer 1102. It should be noted that theprotection layer formed on the sidewalls can be replaced by othermaterials such as photoresist, polymer and the like.

FIG. 12 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 11 after an etching process is applied to the carrier inaccordance with an embodiment. Portions of the substrate 902 may beremoved to form cavities 1202 by an etching process. The etching processmay be any suitable etching processes such as isotropic silicon etchingprocesses. The protection layers on the sidewalls of the opening 1002(shown in FIG. 11) prevent the etching process from damaging the siliconmembranes 1204, 1206 and 1208. The remained silicon membranes 1204, 1206and 1208 help to improve the bonding ratio of a fusion bonding process,which will be described below with respect to FIG. 14.

FIG. 13 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 12 after an oxide removal process is applied to thecarrier in accordance with an embodiment. As shown in FIG. 13, the oxidelayer shown in FIG. 12 has been removed through a suitable removalprocess such as a wet etch process. The removal process is applied tothe top surface of the carrier until the substrate is exposed. It shouldbe noted the oxide removal is an optional step. A fusion bonding processis capable of bonding a carrier with an oxide bonding interface layerwith a MEMS device.

FIGS. 14-18 illustrate intermediate steps of bonding the MEMS device ontop of the carrier in accordance with an embodiment. FIG. 14 illustratesa cross sectional view of a semiconductor device having a MEMS devicestacked on top of a carrier. The MEMS device and the carrier may bebonded together through suitable bonding techniques such as fusionbonding, anodic bonding, eutectic bonding and the like. In accordancewith an embodiment, the MEMS device and the carrier may be bondedtogether by a fusion bonding process between the bonding interface layer802 (on MEMS device) and the top surface of the carrier.

FIG. 15 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 14 after a thinning process is applied to the top surfaceof the MEMS device in accordance with an embodiment. A grinding processmay be performed on the top side of the MEMS device as shown in FIG. 15.The grinding process is performed until a desired thickness is achieved.In accordance with an embodiment, the MEMS device is of a thickness in arange from about 5 um to about 60 um.

An oxide layer 1502 is deposited on top of the MEMS device throughsuitable fabrication techniques such as CVD or the like. The oxide layer1502 is then patterned according to the location of connection plugs1504 and mechanical bumps 1506. An etching step is then performed toetch through the oxide layer 1502 to form a plurality of openings forthe connection plugs 1504 and mechanical bumps 1506. A conductive layer(not shown) formed of polysilicon is deposited on top of the oxide layer1502. The conductive material is filled into the openings to formcontact plugs 1504 and mechanical bumps 1506. As shown in FIG. 15, thecontact plugs 1504 are electrically coupled to the substrate. A CMPprocess may be employed to remove the conductive layer on top of theMEMS device. The CMP process is performed until the oxide layer 1502 isexposed.

FIG. 16 illustrates the formation and patterning of a bonding materiallayer on top of the MEMS device in accordance with an embodiment. Thebonding material layer is formed over the oxide layer 1502. The bondingmaterial 1602 may be made of aluminum copper, germanium, gold, the like,or a combination thereof. The bonding material 1602 may be formed usingPVD, such as sputtering or evaporation, the like, a combination thereof,or other acceptable methods. The bonding material layer 1602 may bepatterned using acceptable lithography techniques. In addition, anover-etching process may be employed to remove a portion of the poly1506 to form the mechanical bump 1604 as shown in FIG. 16.

FIG. 17 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 16 after the MEMS device's structure is defined inaccordance with an embodiment. Portions of the oxide layer and thesubstrate of the MEMS device are removed to define the MEMS structure.As shown in FIG. 17, the substrate of the MEMS device has been dividedinto several isolated regions by a plurality of deep openings 1702.

FIG. 18 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 17 after a vapor HF process is applied to the MEMS devicein accordance with an embodiment. The oxide layers of the MEMS devicefunction as sacrificial oxide layers. The sacrificial oxide layers maybe subject to a HF vapor etching process. As a result, portions of thesacrificial oxide layers are removed. It should be noted that thesacrificial oxide layers to be removed depend on the layout design.

As shown in FIG. 18, anchor regions such as anchor region 1802 may beprotected by the polysilicon plugs. After the HF vapor etching process,sealed cavities of the carrier such as cavity 1806 are connected to theopenings of the MEMS device. One advantageous feature of having a vaporHF etching process is that the dry releasing process from the HF vaporhelps to reduce the occurrence of a well-known MEMS fabrication issue,namely the stiction problem.

FIGS. 19-21 illustrate intermediate steps of bonding a CMOS device ontop of the MEMS device in accordance with an embodiment. FIG. 19illustrates the formation and patterning of a bonding material layer onthe CMOS device in accordance with an embodiment. The CMOS device maycomprise a substrate. The substrate may further comprise a variety ofelectrical circuits (not shown). The electrical circuits formed on thesubstrate may be any type of circuitry suitable for a particularapplication. In accordance with an embodiment, the electrical circuitsmay include various n-type metal-oxide semiconductor (NMOS) and/orp-type metal-oxide semiconductor (PMOS) devices such as transistors,capacitors, resistors, diodes, photo-diodes, fuses and the like. Theelectrical circuits may be interconnected to perform one or morefunctions. The functions may include memory structures, processingstructures, sensors, amplifiers, power distribution, input/outputcircuitry or the like. One of ordinary skill in the art will appreciatethat the above examples are provided for illustrative purposes only tofurther explain applications of the present disclosure and are not meantto limit the present disclosure in any manner

The bonding material layer 1902 is formed over the substrate of the CMOSdevice. In accordance with an embodiment, the bonding material layer1902 may be made of aluminum copper, germanium, gold, the like, or acombination thereof. The bonding material layer 1902 may act as aeutectic bonding material for subsequent bonding processes. The bondingmaterial 1902 may be formed using PVD or other acceptable methods, andmay be patterned using acceptable lithography techniques.

FIG. 20 illustrates a cross sectional view of a semiconductor devicehaving a CMOS device stacked on top of a MEMS device in accordance withan embodiment. The CMOS device 300 is bonded on top of the MEMS device100. The two structures may be bonded together by eutectic bondingbetween the bonding material 1602 (on MEMS device 100) and bondingmaterial 1902 (on CMOS device 300). As shown in FIG. 20, through theeutectic bonding process, movable elements (e.g., movable element 2006)may be located between a top electrode 2004 and a bottom electrode 2002.

In accordance with an embodiment, a bond force of larger than 30 kN anda temperature of larger than 400° C. can be applied to get a good bondstrength. According to an embodiment, a vacuum chamber may be used as abonding chamber. However, according to another embodiment, the bondingchamber has atmospheric pressure.

FIG. 21 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 20 after a grinding process is applied to thesemiconductor device in accordance with an embodiment. A grindingprocess is applied to the bottom side of the carrier 200 until the inputand output pads 2102 and 2104 are exposed. The input and output pads2102 and 2104 are electrically coupled to the integrated circuits of theCMOS device 300. In addition, the input and output pads 2102 and 2104may further be coupled to external circuits (not shown).

FIGS. 22-44 illustrate intermediate steps of fabricating a MEMS devicein accordance with another embodiment. The fabrication steps of the MEMSdevice and the carrier shown in FIGS. 22-34 are similar to thefabrication steps shown in FIGS. 2-14, and hence are not discussed againto avoid unnecessary repetition.

FIG. 35 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 34 after a plurality of through openings are formed in thesubstrate of the MEMS device in accordance with an embodiment. Athinning process is performed on the top surface of the MEMS device. Thegrinding is performed until a desired thickness is achieved. Inaccordance with an embodiment, the MEMS device is of a thickness in arange from about 5 um to about 60 um.

An etch step is then performed to etch through substrate of the MEMSdevice to form through-openings 3502. The etch step may be performedusing DRIE. Through-openings 3502 may physically and electricallyisolate some portions (e.g., portion 3504) of substrate from otherportions (e.g., portion 3506) of the substrate.

FIG. 36 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 35 after an oxide deposition is applied to thesemiconductor device in accordance with an embodiment. The oxidedeposition may form a sacrificial oxide layer 3602. The sacrificialoxide layer 3602 can be formed by any suitable fabrication techniquessuch as CVD, LPTEOS, PECVD, HDPCVD and the like. It should be noted thatthe sacrificial oxide layer 3602 may be formed through multiple oxidedeposition processes and their corresponding etch-back processes. Inaddition, as shown in FIG. 36, there may be an air opening 3604 formedin the sacrificial oxide layer 3602.

FIG. 37 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 36 after a patterning process is applied to thesacrificial oxide layer in accordance with an embodiment. The patterningprocess is employed to form openings 3702 in the sacrificial oxide layer3602. The patterning process may be accomplished by depositing acommonly used mask material (not shown) such as photoresist over thesacrificial oxide layer 3602. The mask material is then patterned andthe sacrificial oxide layer 3602 is etched in accordance with thepattern to form the openings 3702.

FIG. 38 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 37 after a polysilicon layer is formed on the sacrificialoxide layer in accordance with an embodiment. A layer of polysilicon3802 is formed over the structure, including within openings 3702 (notshown but illustrated in FIG. 37). As shown in FIG. 38, the polysiliconlayer 3802 not only fills the openings 3702, it also covers the topsurface of the MEMS device.

FIG. 39 illustrates the formation and patterning of a bonding materiallayer on top of the MEMS device in accordance with an embodiment. Thebonding material layer 3902 may be made of aluminum copper, germanium,gold, the like, or a combination thereof. The bonding material 3902 maybe formed using PVD and the like. The bonding material 3902 may bepatterned using acceptable lithography techniques.

FIG. 40 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 39 after an etching process is applied to the polysiliconlayer in accordance with an embodiment. A patterning process is appliedto the polysilicon layer 3802 (shown in FIG. 38) by depositing acommonly used mask material (not shown) such as photoresist. The maskmaterial is then patterned and the polysilicon layer 3802 is etched backto remove portions of polysilicon layer 3802 overlying the MEMS device,while leaving polysilicon plugs, such as plug 4004 and openings 4002.

FIG. 41 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 40 after a vapor HF process is applied to the sacrificialoxide layer in accordance with an embodiment. The fabrication step ofFIG. 41 is similar to the fabrication step described above with respectto FIG. 17, and hence is not discussed in further detail to avoidunnecessary repetition.

FIGS. 42-44 illustrate intermediate steps of bonding a CMOS device ontop of the MEMS device in accordance with an embodiment. The steps ofbonding the CMOS device on top of the MEMS device are similar to thosedescribed above with respect FIGS. 18-20, and hence are not discussedagain herein.

FIGS. 45-52 illustrate intermediate steps of fabricating a MEMS devicein accordance with another embodiment. The fabrication steps illustratedin FIGS. 45-52 are applicable to other semiconductor structures such asforming interconnects of the MEMS device including electrical readoutsand the like.

FIG. 45 illustrates a cross sectional view of a semiconductor devicesimilar to the semiconductor devices shown in FIG. 12 and FIG. 32 aftera further anisotropic etching process is applied to a carrier inaccordance with some embodiments. The carrier 4502 shown in FIG. 45 issimilar to the carrier 200 shown in FIG. 1A. The substrate 4504 of thecarrier 4502 may be formed of the same material as the substrate 902shown in FIG. 9. In accordance with an embodiment, the substrate 4504 isa low resistive silicon substrate.

As shown in FIG. 45, portions of the substrate 4504 are removed to formtrench and via extrusions over cavities 4506. An etching process, suchas a reactive ion etch (RIE) or other dry etch, an anisotropic wet etch,or any other suitable anisotropic etch or patterning process, may beperformed to form the trench and via extrusions over the cavities 4506.The trench and via extrusions are used to form electrical readoutinterconnects for the MEMS device, which will be described below withrespect to FIG. 52.

FIG. 46 illustrates a cross sectional view of the semiconductor deviceafter the trench and via openings shown in FIG. 45 are sealed by adielectric layer in accordance with an embodiment. The dielectric layer4602 may be formed, for example, of a low-K dielectric material, such assilicon oxide. In accordance with an embodiment, the dielectric layermay be an oxide layer formed by suitable semiconductor fabricationtechniques such as a CVD process and the like.

FIG. 47 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 46 after forming contact vias in the dielectric layer inaccordance with an embodiment. A plurality of contact vias 4702 may beformed in the dielectric layer 4602 through a patterning process. Thecontact vias may be formed of suitable metal materials such as tungstenand the like.

FIG. 48 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 47 after depositing and patterning a bonding layer on theoxide and the contact vias in accordance with an embodiment. The bondinglayer 4802 may be formed of germanium and the like. The bonding layer4802 is patterned to expose cavities for pressure reduction.

FIG. 49 illustrates a cross sectional view of the semiconductor deviceafter a MEMS device is bonded on top of the semiconductor device shownin FIG. 48 in accordance with an embodiment. Before a bonding process isapplied to the MEMS device and the semiconductor device, a bonding layercomprising suitable bonding materials such as aluminum copper may bedeposited and patterned on the MEMS device 4902. Through a suitablebonding process such as a eutectic bonding process, a conductive bondinginterface is established between the semiconductor device and the MEMSdevice 4902. For example, the bonding interface may comprise a eutecticalloy formed by a eutectic bonding reaction between a first bondinglayer comprising germanium and a second bonding layer comprising analuminum copper alloy.

FIG. 50 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 49 after a grinding process is applied to thesemiconductor device in accordance with an embodiment. A grindingprocess is applied to the non-bonding side of the carrier 4502 until thetrench and via extrusions are exposed. The grinding process may beimplemented by suitable grinding techniques including silicon grinding,chemical mechanical polishing, etching and the like.

FIG. 51 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 50 after sealing the trench and via openings with adielectric layer and patterning the dielectric layer to formcontact-to-silicon vias in accordance with an embodiment. The dielectriclayer 5102 may be an oxide layer. The oxide layer may be suitablesemiconductor fabrication techniques such as CVD and the like.

FIG. 52 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 51 after electrical readout structures are formed over thenon-bonding side of the carrier in accordance with an embodiment.Conductive materials such as an aluminum copper alloy are deposited onthe non-bonding side of the carrier through suitable depositionprocesses such as CVD, PVD and the like. The conductive material layeris further patterned to form electrical readout structures 5202 as shownin FIG. 52.

FIG. 53 illustrates a cross sectional view of a semiconductor device inaccordance with another embodiment. The structure of the semiconductordevice 5302 is similar to the semiconductor device shown in FIG. 52except that the substrate 5304 of the semiconductor device 5302 does notinclude cavities. In other words, the isotropic etching processillustrated in FIGS. 12 is not applied to the substrate 5304. Otherfabrication steps for forming the semiconductor device 5302 shown inFIG. 53 are similar to those described above with respect to FIGS.46-52, and hence are not discussed again herein.

FIG. 54 illustrates a cross sectional view of a semiconductor device inaccordance with yet another embodiment. The structure of thesemiconductor device 5402 is similar to the semiconductor device shownin FIG. 51 except that the trench and via openings are sealed by anoxide layer 5404 and an aluminum copper layer 5406.

FIG. 55 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 54 after a patterning process is applied to thenon-bonding side of the carrier in accordance with an embodiment. Apatterning process is applied to the oxide layer 5404 as well as thealuminum copper layer 5406 to form contact-to-silicon vias 5502.

FIG. 56 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 55 after a conductive material is deposited to formelectrical readout structures in accordance with an embodiment.Conductive materials such as aluminum copper may be deposited on thecontact-to-silicon vias 5502 to form electrical readout structures 5602of the MEMS device.

Although embodiments of the present disclosure and its advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the present disclosure, processes, machines,manufacture, compositions of matter, means, methods, or steps, presentlyexisting or later to be developed, that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein may be utilized according to the presentdisclosure. Accordingly, the appended claims are intended to includewithin their scope such processes, machines, manufacture, compositionsof matter, means, methods, or steps.

What is claimed is:
 1. A semiconductor device comprising: a carrierhaving a plurality of cavities; a micro-electro-mechanical system (MEMS)substrate bonded on the carrier, where the MEMS substrate comprises: afirst side bonded on the carrier; a shielding layer formed over thefirst side and coupled to ground; a plurality of vias coupled betweenthe shielding layer and bottom electrodes of the MEMS substrate; amoving element located between a top electrode and a bottom electrode;and a second side having a plurality of bonding pads; and asemiconductor substrate bonded on the MEMS substrate.
 2. Thesemiconductor device of claim 1, wherein: the MEMS substrate comprises aplurality of air channels coupled to the cavities of the carrier.
 3. Thesemiconductor device of claim 1, wherein: each cavity of the pluralityof cavities comprises an extrusion.
 4. The semiconductor device of claim1, further comprising: a first dielectric layer deposited on the firstside of the MEMS substrate; a vapor HF stop layer formed over thedielectric layer; a second dielectric layer formed over the vapor HFstop layer; and a bonding layer formed over the second dielectric layer.5. The semiconductor device of claim 4, where: the first dielectriclayer is a first oxide layer; the vapor HF stop layer is a low stressnitride layer; the second dielectric layer is a second oxide layer,wherein the plurality of vias are formed in the second dielectric layer;and the bonding layer is formed of polysilicon.
 6. The semiconductordevice of claim 1, further comprising: a CMOS bonding layer on thesemiconductor substrate, wherein the CMOS bonding layer is conductive.7. The semiconductor device of claim 1, further comprising: a conductivelayer formed between the semiconductor substrate and the MEMS substrate,wherein the conductive layer is thinner than the MEMS substrate.
 8. Thesemiconductor device of claim 1, wherein: a first side of a cavity ofthe carrier is sealed by a first sealing layer; and a second side of thecavity of the carrier is sealed by a second sealing layer, wherein thesecond side of the cavity is a nonbonding side of the carrier.
 9. Thesemiconductor device of claim 8, wherein: the first sealing layer is afirst oxide layer; and the second sealing layer is a second oxide layer.10. The semiconductor device of claim 8, wherein: the first sealinglayer is a first oxide layer; and the second sealing layer comprising: asecond oxide layer; and an aluminum layer formed over the second oxidelayer.
 11. The semiconductor device of claim 8, further comprising: anelectrical readout structure formed over the second side of the cavityof the carrier.
 12. A method comprising: providing amicro-electro-mechanical system (MEMS) substrate having: a shieldinglayer coupled to ground; a plurality of vias coupled to the shieldinglayer; and a sacrificial layer on a first side; providing a carrierincluding a plurality of cavities; bonding the first side of the MEMSsubstrate on the carrier; forming a first bonding material layer on asecond side of the MEMS substrate; applying a sacrificial layer removalprocess to the MEMS substrate; providing a semiconductor substrateincluding a second bonding material layer; and bonding the semiconductorsubstrate on the second side of the MEMS substrate.
 13. The method ofclaim 12, further comprising: depositing a first dielectric layer on thefirst side of the MEMS substrate; depositing a vapor HF stop layer onthe first dielectric layer; depositing a second dielectric layer on thevapor HF stop layer, wherein the plurality of vias are formed in thesecond dielectric layer; and forming a bonding layer on the seconddielectric layer.
 14. The method of claim 12, further comprising:depositing a third dielectric layer on the carrier; forming a pluralityof openings in the carrier through an etching process; forming adielectric protection layer on sidewalls of the openings; and enlargingthe openings through an isotropic etching process.
 15. The method ofclaim 12, further comprising: forming a plurality of MEMS openings inthe MEMS substrate from the second side of the MEMS substrate;depositing a third dielectric layer to fill the MEMS openings; forming athin conductive layer on the third dielectric layer; forming the firstbonding material layer on the thin conductive layer; and patterning thethin conductive layer to form a plurality of conductive elements andmovable elements.
 16. The method of claim 12, further comprising:sealing a first side of a cavity of the carrier with a first sealinglayer; applying a thinning process to a second side of carrier until asecond side of the cavity is exposed, wherein the second side of thecarrier is a nonbonding side of the carrier; and sealing the second sideof the cavity with a second sealing layer.
 17. The method of claim 16,further comprising: forming an electrical readout structure over thesecond side of the carrier.
 18. A method comprising: providing amicro-electro-mechanical system (MEMS) device including: forming a firstsacrificial dielectric layer having a plurality of sealed trenches on afirst side of the MEMS substrate; forming a plurality of electrodes andmechanical bumps on the first sacrificial dielectric layer; depositing avapor HF stop layer on the first sacrificial dielectric layer;depositing a second sacrificial dielectric layer on the vapor HF stoplayer; forming a plurality of vias in the second sacrificial dielectriclayer; and forming a bonding layer on the second sacrificial dielectriclayer, wherein the bonding layer is coupled to ground and the pluralityof vias are coupled between the bonding layer and the plurality ofelectrodes; providing a carrier including a plurality of cavities;bonding the first side of the MEMS substrate on the carrier; forming afirst bonding material layer on a second side of the MEMS substrate;applying a sacrificial layer removal process to the MEMS substrate;providing a semiconductor substrate including a second bonding materiallayer; and bonding the semiconductor substrate on the second side of theMEMS substrate.
 19. The method of claim 18, further comprising:depositing an oxide material on the first side of the MEMS substrate;patterning the oxide material to form a plurality of trenches; anddepositing the oxide material on the trenches to form the sealedtrenches.
 20. The method of claim 18, further comprising: forming aplurality of MEMS openings in the MEMS substrate from the second side ofthe MEMS substrate; depositing a third dielectric layer to fill the MEMSopenings; forming a thin conductive layer on the third dielectric layer;forming the first bonding material layer on the thin conductive layer;and patterning the thin conductive layer to form a plurality ofconductive bumps and mechanical structures.